This proposal details a methodological study into the synthetic applications of peroxides. These studies serve two major purposes. First, they would provide new information on the reactivity of peroxides and the stereochemical consequences of their reactions. Second, they would illustrate the design of systems which could fully exploit the usefulness of the reactions of peroxides in the synthesis of a large body of biologically important natural products. New approaches to the synthesis of macrolide and ionophoric natural products, compounds which often exhibit significant antibacterial or antiviral activity, are described. In addition, new methods to construct the endoperoxide nucleus of the key prostaglandin endoperoxides, PGH2 and PGG2, are described.